AudioCircle
Industry Circles => Tortuga Audio => Topic started by: tortugaranger on 6 Apr 2015, 06:04 pm
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After 3+ years of iterative development of our LDR passive preamp technology and related preamp models, it's time to make some decisions on what to focus on next. To that end, I would welcome your feedback, thoughts, suggestions etc. While I have my own product ideas and preferences, what matters in the end is what are YOU interested in seeing and what are your friends interested in and what do you think everyone else might be interested in. So consider this a wish list request. Opine and wish away!
I'll seed this with a few thoughts:
1) Version V3 of the LDR3x Preamp Controller Board. - This would involve a complete hardware redesign utilizing surface mount components resulting in a much smaller board. One possibility is the complete separation of the digital controller from the analog wherein a single digital controller board would interface with multiple LDR boards with each LDR board providing a stereo channel. For example, a typical singled ended stereo preamp would have 1 controller board and 2 LDR boards. A 2x5 ribbon cable would connect from the controller to each LDR boards. For a balanced system you would have 4 LDR boards. You could just keep adding channels to get a 7.1 systems. The V3 might also have a new companion display module with would be LCD screen rather than 7 segment numerals. The V3 or close variant would likely be a candidate for OEM version for use by other manufacturers.
2) Buffered LDR Preamp - Technically this would not be a "passive" preamp since the output of the LDR attenuator would feed into high impedance buffer stage which could have unity gain or perhaps optional gain boost. The presumptive benefit of a buffer would be improved dynamics for those systems where a passive isn't the best fit. More than likely this would be a solid state buffer with a high current delivery capacity. We've been noodling on this for quite some time and are currently favoring TI's LME49600 buffer chip. This buffer would be an optional add-on to the existing line of preamps, possibly also a retrofit option, and could also be a true stand alone buffer product without a front-end LDR attenuator.
3) Integrated Headphone Amp - Turns out that the buffer design we're pursuing is also an excellent candidate for a headphone amp with the addition of appropriate gain plus an output disconnect safety circuit to prevent feeding excess DC offset into the headphones (due to excess external offset from source or internally generated offset from power supply failure/imbalance etc. ). While headphone amps is a crowded market, we would have the key differentiator of being the ONLY one with an LDR front end with all the commensurate sonic benefits relative to all the others with volume pots. Also, our headphone preamp will a true balanced design with a pair of amps driving each channel for a total of 4 amps per headphone. Of course it would also have a conventional single-ended output.
4) Phono stage/preamp - I have a working prototype that I've listening to for the past few weeks connected with a high output (2.5 mv) moving coil cartridge with excellent results - to my ears at least. Just like the buffer option, the phono stage could be an option for out existing LDR preamp product line that would allow direct connection of turntables to our preamps without the need for a separate phono stage. This would probably start off as being compatible only with MM and high output MC cartridges. Low output MC cartridges require additional design considerations we've yet to tackle. I'm of the opinion that most audiophiles find the "phono stage" to be a bit mysterious but it's actually quite a straight forward device. It's basically an active filter (with gain) to correct for the RIAA standard frequency bias baked into all vinyl records starting way back in the 50's or thereabouts. And of course it has to also boost the low millivolt level output of the phono cartridge to typical line level voltage (~2 volt RMS) needed by downstream premaps/amps.
5) Fully integrated amp - Here we'd marry the existing LDR preamp plus buffer plus phono stage with our own amp which might be chip-amp variant of the LM4780 run in parallel for somewhere around an 80-100 watt output. Of all the above ideas, this is my least favorite since it goes against my audiophile grain of separate components. Yet I've had a few inquiries asking for this so I could be totally wrong about this from a marketing standpoint. Noticeably absent from this list of features is an integrated DAC. A DAC is one thing we will not seek to develop in-house. But licensing an existing DAC design/board is always a possibility.
Thanks for reading all this and double thanks for offering your input.
Cheers,
Morten :thumb:
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I think that where you started - with the benefits of a passive unit using LDR's is where to stick. As soon as you add active circuitry you have moved away from that "keep it simple" philosophy. But it does have the advantage if the output cable runs are long, and cable capacitance loading is an issue.
I like the first option a lot - it changes the architecture only, with potential benefits of simplicity and flexibility.
A further option that might be worth adding to balanced units is phase invert.
Cheers
Craig
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I like all your ideas, but I like Option 1 the most especially if we can design a 7.1 or 7.2 LDR based attenuator without fancy digital manipulation that is common in high end AVP's. Just a simple volume control. The ability to trim each channel (+/- 10 dB in 1 dB steps) would be awesome. Buffer stages can be added if needed of course.
Regarding Option 4, I've sent you a PM.
Best,
Anand.
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Since you asked :)
I don't think you should obsolete your V2 board already, it's less than year since it came out.
I do think multichannel would be interesting. I don't think you should be thinking "7.1" but "any number." The trim idea from Anand would also be very interesting, but I think you can do "-" only. I think this would also need a way to program in the impedance of the output device, so that channels stay matched across the range. (i.e. you can't assume that all channels are driving the same impedance if you really want this to work well.)
I think that an inter-chassis solution would be very interesting. That way attenuators could be built into amps, and all controlled from the... er controler.
A single front panel rather than bits and pieces seems like a logical thing to do.
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I think that where you started - with the benefits of a passive unit using LDR's is where to stick. As soon as you add active circuitry you have moved away from that "keep it simple" philosophy. But it does have the advantage if the output cable runs are long, and cable capacitance loading is an issue.
I like the first option a lot - it changes the architecture only, with potential benefits of simplicity and flexibility.
A further option that might be worth adding to balanced units is phase invert.
Cheers
Craig
Thanks Craig. I agree with you as a technical matter but as a commercial/marketing matter I suspect there's a hard core faction of audiophiles who view passives as inherently less good than an active premap. It's an undeniable part of being human that our strongly held views are often the very thing that prevents us from trying alternatives that may challenge those views. Any active preamp (or any audio unit with a volume control) could benefit from LDR attenuation. The question comes down to this. As an audio company should we continue to solely promote our core LDR passives or also offer a buffered (a.k.a. active) version of same product for those who wouldn't touch a passive with a 10 foot pole?
Best,
Morten :thumb:
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I like all your ideas, but I like Option 1 the most especially if we can design a 7.1 or 7.2 LDR based attenuator without fancy digital manipulation that is common in high end AVP's. Just a simple volume control. The ability to trim each channel (+/- 10 dB in 1 dB steps) would be awesome. Buffer stages can be added if needed of course.
Regarding Option 4, I've sent you a PM.
Best,
Anand.
Thanks Anand. Your insights are welcomed and valuable as always. Done properly a single controller board would interface with any number of LDR board/channels. With a 7.2 system you're looking at possibly 9 channels which if each LDR board is a 2 channel unit this would require 5 boards each with either a 10 or 14 pin ribbon cable connector back to the controller board. All doable with enough controller board real estate and header pins.
Your PM suggestion regarding amp options is well taken. Less reinventing of the wheel thank you.
Best,
Morten
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Since you asked :)
I don't think you should obsolete your V2 board already, it's less than year since it came out.
As a practical matter I don't think we'll be ready with a V3 for another year or so. Also, I don't expect any future iteration of our LDR preamp boards to have materially improved sound over our existing designs - but of course I could be wrong about that. :green: I view it as a design refinement based on everything we've learned to date that will broaden its potential application.
I do think multichannel would be interesting. I don't think you should be thinking "7.1" but "any number." The trim idea from Anand would also be very interesting, but I think you can do "-" only. I think this would also need a way to program in the impedance of the output device, so that channels stay matched across the range. (i.e. you can't assume that all channels are driving the same impedance if you really want this to work well.)
The multi-channel is quite doable. Achieving uniform output impedance from multiple passive L-pad attenuators would be truly challenging if not impossible without using output buffers.
I think that an inter-chassis solution would be very interesting. That way attenuators could be built into amps, and all controlled from the... er controler.
Eventually we hope to have a suitable OEM version that could work well anywhere an attenuator is needed along with input switching and remote control. We welcome inquiries and I'm sure this will end up involving a bit of collaboration before it becomes a reality.
A single front panel rather than bits and pieces seems like a logical thing to do.
Yes, the control features/options have outgrown a simple remote and a 2/4 digit display.
Best,
Morten
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I really like option 2, primarily for the impedance matching it would provide.
Wyred 4 Sound makes, essentially, what you're considering (with the exception of the type of attenuation used) with their STP-SE.
What I'd personally like to see is a tube buffer option. The only preamps / buffers I've seen with this configuration are those by Gary Dodd and one of the selectable configurations in Red Wine's new LIO.
Could you offer both a tube buffer and SS buffer, perhaps in the same unit so the user can select per their preference? What'd be killer is if the buffer(s) could also be bypassed entirely. This would be a game changing 3-in-1 design. :o
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Everyone seems to want something a little different than each other. Perhaps a modular architecture could make everyone happy, including Morten? :D
I think a phono stage with high enough gain to drive most amps would be a fine idea. If you do build a phono unit, please include a mono switch!
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Melos comes to mind. Using your excellent LDR volume controls with a tubed linestage would be inviting. For the SS crowd no tube just linestage.
charles
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What I'd personally like to see is a tube buffer option.
We've been working a 6SN7/6CG7 tube buffer design for a while now. The trick is getting them to be stone cold quiet which I believe we've accomplished. The SS vs. Tube buffer comes down to cost vs. value with tubes always costing more due to power supply requirements and DC offset protection.
Could you offer both a tube buffer and SS buffer, perhaps in the same unit so the user can select per their preference? What'd be killer is if the buffer(s) could also be bypassed entirely. This would be a game changing 3-in-1 design. :o
While this would make for an interesting demo unit I believe it presents an awkward choice commercially and may ultimately confuse most buyers. And it would definitely drive up the cost. Offering both flavors separately is a possibility.
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I think a phono stage with high enough gain to drive most amps would be a fine idea.
I'm not sure a "one gain fits all" approach would work since there's a fairly wide range of output voltages depending on make, model, type of cartridge. Just maxing out the gain for all possibilities will likely disappoint. The higher the gain the higher the signal to noise ratio. Then there's special design considerations for MC (moving coil) cartridges which tend to have very low output of only a few tenth's of a millivolt vs. MM (moving magnet) cartridges with up to 5 millivolt of output. Over a an order of magnitude range.
If you do build a phono unit, please include a mono switch!
Easy enough to do but I'd like to understand better why you'd find this desireable.
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Eventually we hope to have a suitable OEM version that could work well anywhere an attenuator is needed along with input switching and remote control. We welcome inquiries and I'm sure this will end up involving a bit of collaboration before it becomes a reality.
I guess I didn't explain my suggestion very well. I was thinking about DIY boards, where the attenuator modules could be built into amps. Then several amps could be controlled from the one controller.
Just an idea :)
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I'm not sure a "one gain fits all" approach would work since there's a fairly wide range of output voltages depending on make, model, type of cartridge. Just maxing out the gain for all possibilities will likely disappoint. The higher the gain the higher the signal to noise ratio. Then there's special design considerations for MC (moving coil) cartridges which tend to have very low output of only a few tenth's of a millivolt vs. MM (moving magnet) cartridges with up to 5 millivolt of output. Over a an order of magnitude range.
Easy enough to do but I'd like to understand better why you'd find this desireable.
No, you would have to have some gain choices to be sure. My current phono unit has choices between 48, 60, & 70dB. Even though the 70 setting is enough gain for my Denon DL-103 at .003 mV, it still sounds better at 48dB with a 23dB step up transformer. I don't know why this would be, but I know I'm not the only one that prefers a lower gain phono setting with a SUT.
The reason for including a mono switch, is mono LP's! Mono LP's sound better played summed, even with a stereo cartridge. Playing summed lowers the surface noise dramatically, and renders a smoother top end. A simple double Y connector/adapter can show you the difference easily, even with all those extra connections. It is most effective between the phono unit & preamp. Placing the summing cord before the phono unit can/will change the cartridge load, which is not advisable.
Many of the classic jazz albums were cut in mono. And don't forget the recent Beatles mono box set! Ortofon came out with the 2M White mono cartridge just for that release!
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I would do an active solid state buffer and and active tube stage with gain. The National part is great but sonically even better is a Lsk170 biased via another LSK170 acting as current source. You can match them to get zero offset or use a lower IDSS part as the buffer and a higher IDSS part as the current source and trim the current source to get zero offset. You could also try paralleling them for more drive. A single jfet has 50 ohm output impedance so two in parallel would get you 25 ohm. The fet is slightly more lucid and real than the National buffer. I use the jfets in my Oppo mods on the output of the ESS DACs. For best sound the National buffer needs to be biased for maximum speed and I use .15 modified Wima bypass caps right on the pins to keep them stable.
An active tube line stage would give added gain and give the liquid and palpable sound some people crave. The tube stage would have to have great regulators, resistors, power supply caps and output caps.....much more expensive.
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I would do an active solid state buffer and and active tube stage with gain. The National part is great but sonically even better is a Lsk170 biased via another LSK170 acting as current source. You can match them to get zero offset or use a lower IDSS part as the buffer and a higher IDSS part as the current source and trim the current source to get zero offset. You could also try paralleling them for more drive. A single jfet has 50 ohm output impedance so two in parallel would get you 25 ohm. The fet is slightly more lucid and real than the National buffer. I use the jfets in my Oppo mods on the output of the ESS DACs. For best sound the National buffer needs to be biased for maximum speed and I use .15 modified Wima bypass caps right on the pins to keep them stable.
An active tube line stage would give added gain and give the liquid and palpable sound some people crave. The tube stage would have to have great regulators, resistors, power supply caps and output caps.....much more expensive.
Thanks for the input Ric. I've not worked with the lsk170's but I've heard they are popular. I ran a few sims of this with a split voltage supply and also used an op amp servo to null out any output offset (regardless of IDSS mismatch) by feeding the servo out back into the gate to trim things out. This could potentially eliminate the big output coupling cap which I would think is big plus sonically. With this approach I'd probably also want to have DC offset safety disconnect relay just in case things went wacky upstream with the power supply, jfets etc.
Curious why you'd want to add gain with the tube stage at all...or...why with tubes and not SS? I reread your note and realize you were suggesting putting the fet buffer TOGETHER with a tube stage with gain as a package. :duh:
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I think a popular product would be a simple volume control in its own enclosure with a remote. I believe there are many people that won't buy a preamp if it doesn't have a remote for volume, me included. The manufacturers of these preamps choose for whatever reason, may it be cost or sound quality not to add a remote.
This would simply be an additional product in your line up prebuilt or DIY but one that I believe would be a good seller and capture the market that you're otherwise not tapping, which of course are people that don't want a passive preamp.
Just my .02 cents.
Greg
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I think a popular product would be a simple volume control in its own enclosure with a remote. I believe there are many people that won't buy a preamp if it doesn't have a remote for volume, me included. The manufacturers of these preamps choose for whatever reason, may it be cost or sound quality not to add a remote.
This would simply be an additional product in your line up prebuilt or DIY but one that I believe would be a good seller and capture the market that you're otherwise not tapping, which of course are people that don't want a passive preamp.
Just my .02 cents.
Greg
You should probably read the first post of the thread (re: buffered preamp). :thumb:
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You don't need any coupling caps with the jfet buffers. Please see this thread: http://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer.html for info on the circuit and using shunt regulators. You don't need an output resistor either.
No, I was not suggesting using a solid state buffer with a tube line stage....but two separate products....a solid state buffered unit for lower output impedance and a separate tube output stage version (offering gain and buffering and the highly desired tubey sound).
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You should probably read the first post of the thread (re: buffered preamp). :thumb:
This is not what I was talking about. When I had the original LDR3 in my system while it was on tour I was able to test it with an amp that had a volume control. Whether I listened to the amp with the LDR in the system or out of the system I couldn't here a difference. That's why I think using an LDR as a volume control only would be a great product, no gain, just a remote volume control for any active preamp that doesn't have one.
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You don't need any coupling caps with the jfet buffers. Please see this thread: http://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer.html for info on the circuit and using shunt regulators. You don't need an output resistor either.
No, I was not suggesting using a solid state buffer with a tube line stage....but two separate products....a solid state buffered unit for lower output impedance and a separate tube output stage version (offering gain and buffering and the highly desired tubey sound).
What you are talking about (your SS suggestion) it seems is the DCB1. This is something I have mentioned to Morten in pm's previously. All info is on diyaudio, and the boards are available at the diyaudio store (or PM Tea-Bag on diyaudio for a version without input selection)complete with shunt regulator supply if you don't want to build breadboards (and I imagine Morten would not). It's a great sounding buffer, but would be better with Morten's LDR :wink:
Best,
Anand.
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This is not what I was talking about. When I had the original LDR3 in my system while it was on tour I was able to test it with an amp that had a volume control. Whether I listened to the amp with the LDR in the system or out of the system I couldn't here a difference. That's why I think using an LDR as a volume control only would be a great product, no gain, just a remote volume control for any active preamp that doesn't have one.
I think there's some confusion regarding your comment so perhaps this will help clarify.
All of our preamps are LDR passive volume controls.
All have no gain.
All have remote control.
Some have input switching.
I believe you are suggesting substituting any active preamp's volume control (typically a potentiometer) with Tortuga LDR volume control (without input switching).
For me the confusion with your comment is that what you are describing is basically what our stuff already is and does. Depending on how it's applied.
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I think there's some confusion regarding your comment so perhaps this will help clarify.
All of our preamps are LDR passive volume controls.
All have no gain.
All have remote control.
Some have input switching.
I believe you are suggesting substituting any active preamp's volume control (typically a potentiometer) with Tortuga LDR volume control (without input switching).
For me the confusion with your comment is that what you are describing is basically what our stuff already is and does. Depending on how it's applied.
Thank you Morten for clarifying what I was saying, I guess it was so simple it was confusing?
Yes, a small box no gain, no additional inputs, just a remote. This would keep the cost down and be for anyone who has a preamp without a remote who likes the sound he is already getting but wishes he had a remote.
Someone just recently sold a Dude preamp and the person said they loved it but just couldn't live without a remote anymore, when I'm looking at buying a new preamp like many others I look to see if a remote is available for it, if not I move on. Like I mentioned it would be an add on product to your line up not a replacement.
I do like the idea of a tube buffer stage as well, many people like adding them for gain or to add tube flavor to their system. And if it has volume control all the better.
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As someone who owns an EVS modded Oppo BDP-105 I would love to replace my active tube pre with a Tortuga Active tube pre with an LDR attenuator for a volume control.I would replace it now but I can't do passive as good as the JFet output stage is on the Oppo it lowered the output voltage.Could one be done with a battery power supply? That would be perfect- an LDR volume controlled active tube pre that runs off a battery supply like the Dodd tube buffer only with an LDR for volume control and just a slight bit of gain.
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As someone who owns an EVS modded Oppo BDP-105 I would love to replace my active tube pre with a Tortuga Active tube pre with an LDR attenuator for a volume control.I would replace it now but I can't do passive as good as the JFet output stage is on the Oppo it lowered the output voltage.Could one be done with a battery power supply? That would be perfect- an LDR volume controlled active tube pre that runs off a battery supply like the Dodd tube buffer only with an LDR for volume control and just a slight bit of gain.
Our first version will be solid state but we have a tube version in the works as well. As it stands now the SS will have an op amp gain stage in front of a JFET buffer - no coupling caps on either the input or output.
I'm a bit skeptical as to how practical powering the tube version with a battery would be due to the higher current draw of tubes not to mention the voltage level. If we went with low voltage "space charge" tubes then it's at least a possibility but I suspect we'd need fairly large batteries. Space charge tubes work fine but tend to have higher distortion levels. We'll definitely look into it before making a final decision.
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How about an app for smartphone/tablet remote control? :eyebrows:
The apple remote works good enough but its very small, easy to lose in the bowels of my Lazy Boy and seems a bit delicate. Also its always good to get rid of one more remote and consolidate.
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Our first version will be solid state but we have a tube version in the works as well. As it stands now the SS will have an op amp gain stage in front of a JFET buffer - no coupling caps on either the input or output.
I'm a bit skeptical as to how practical powering the tube version with a battery would be due to the higher current draw of tubes not to mention the voltage level. If we went with low voltage "space charge" tubes then it's at least a possibility but I suspect we'd need fairly large batteries. Space charge tubes work fine but tend to have higher distortion levels. We'll definitely look into it before making a final decision.
If you were going to use tubes, I would prefer an easier to source tube with good sonics than a Space Charge Tube. NOS tubes are great, but they're becoming more scarce everyday. Some of the new New Sensor tubes tubes sound pretty good, like their 6CG7/6FQ7. I specifically mentioned the 6CG7/6FQ7, as it is one of my favorites. The sound of a 6SN7 without the microphonics!
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How about an app for smartphone/tablet remote control? :eyebrows:
The apple remote works good enough but its very small, easy to lose in the bowels of my Lazy Boy and seems a bit delicate. Also its always good to get rid of one more remote and consolidate.
This is one of our "back burner" projects. The issue isn't designing/coding an app for both iOS and Android but the lack of IR ability is many smartphones. To use your iPhone or iPad for example you would need an additional wifi to IR converter thingy for this to work. Or, we'd have to add a wifi receiver to the next version of the LDR3x board but that would leave all existing boards in the lurch. I occasionally do look into this but have not found the right universal solution - perhaps there isn't one - yet.
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If you were going to use tubes, I would prefer an easier to source tube with good sonics than a Space Charge Tube. NOS tubes are great, but they're becoming more scarce everyday. Some of the new New Sensor tubes tubes sound pretty good, like their 6CG7/6FQ7. I specifically mentioned the 6CG7/6FQ7, as it is one of my favorites. The sound of a 6SN7 without the microphonics!
The 6CG7 (9 pin version of the 6SN7 octal) is my tube of choice for our tube products. I only mentioned the low voltage Space Charge tubes in the context of low voltage (12 V) battery powered.
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I really like the LDR units as they are, so clean & sweet!
I realize that some amps would benefit from a buffer and/or higher gain.
Would it be possible for the out board buffer to offer additional gain too? Perhaps 6dB? Could you have the gain module in the buffer unit, instead of the LDR unit? Or would the extra interconnects negate any advantages?
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Would it be possible for the out board buffer to offer additional gain too? Perhaps 6dB? Could you have the gain module in the buffer unit, instead of the LDR unit? Or would the extra interconnects negate any advantages?
Both buffer types (SS or tube) will have some degree of adjustable gain from unity to +?dB. The gain adjustment will be on the buffer board and will be independent of the upstream LDR attenuator. I don't know yet how we'll handle the gain adjustment. Could use a pot or perhaps even discrete resistors tied to switch. The gain is something you only adjust infrequently to get sufficient volume control headroom.
Physically I think the SS buffer will fit nicely within our existing enclosure designs so can be ordered as a option including a bypass switch. Will probably also package these as stand alone buffer units without any volume control for placement downstream of an existing LDR passive preamp.
The tube version will be physically larger by necessity so will definitely not fit within existing smaller enclosure package. Still sorting that out.
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My 2 cents :)
- Dual grounding scheme for balanced version: play vs calibrate. I did it and it works.
- Shielding the analog path through LDRs from the rest of the board, which is digital.
- Improving the ergonomics of the Apple remote as it is overloaded of functions (use also the enconder + remote for setting impedance, display, calibration, etc.)
- Avoiding to use switching regulators: at least giving this as a paid option, eg using Belleson regulators.
- Making firmware devoted to balanced version as it is different from the single ended version, eg impedance is doubled.
Great job so far, but the path to the hell is still on :) Thanks.
-Roberto
P.S. I am against using buffers, IMHO, as this alters the cool passive nature of Tortuga. A person sold his VTL 7.5 pre (yeah, that expensive VLT pre) as his balanced DAC was more transparent without, so using just the internal volume of the DAC. After trying my balanced DIY Tortuga, probably changed mind... he asked me if the Tortuga had a gain... of course no!
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My 2 cents :)
- Dual grounding scheme for balanced version: play vs calibrate. I did it and it works.
I think I know what you're getting at here but I would ask you to elaborate please.
- Shielding the analog path through LDRs from the rest of the board, which is digital.
To be clear the audio signal path in the existing design is both physically and optically isolated from the analog control path. However to your point the analog control does share a power supply with the digital and these will be separate supplies in the next design iteration.
- Improving the ergonomics of the Apple remote as it is overloaded of functions (use also the enconder + remote for setting impedance, display, calibration, etc.)
I agree and options include: a) Reorganizing certain control functions into a "maintenance mode" which has to be enabled otherwise it operates as a simple remote; b) Moving to a custom remote. This has its advantages but carries a hefty up front capital cost to get unit cost down. Plus the idea of yet another custom IR remote just seems so old school and annoying; c) Moving to a "soft" remote app for both iOS and Android. The biggest obstacle here is the lack of universal built-in IR in all smartphones but this could be done with a simple low-power wifi interface in lieu of IR interface or alternatively an intermediary wifi-to-ir device external to the product itself.
- Avoiding to use switching regulators: at least giving this as a paid option, eg using Belleson regulators.
I will disagree as to the idea that switching regulators are somehow inherently inferior to linear regulators in audio applications. The regulator we currently use is actually quite a nice bit of hardware and far superior to the ubiquitous LM9XXX series we used in the V1 model. That said, it's certainly not a super-regulator like the Belleson. Which by the way we are in the process of evaluating. Also, more recently there are some newer ultra low-noise linear regulators from TI and others that rival super-regulator performance. All of those are surface mount components. Also, anyone daring enough with a solder iron can swap out the existing regulator for a Belleson. Just get one with a LM78xx pin configuration and around 400-500 ma capacity. Be very careful removing the existing regulator which is rather beefy - easy to bugger the pads or lift a trace.
- Making firmware devoted to balanced version as it is different from the single ended version, eg impedance is doubled.
This may best be solved by multiplying by 2 in the interim but I get your point.
P.S. I am against using buffers, IMHO, as this alters the cool passive nature of Tortuga. A person sold his VTL 7.5 pre (yeah, that expensive VLT pre) as his balanced DAC was more transparent without, so using just the internal volume of the DAC. After trying my balanced DIY Tortuga, probably changed mind... he asked me if the Tortuga had a gain... of course no!
In my view there's a small contingent of early adopters who are open to the idea of using passives generally and within that small contingent there's a subset that may eventually discover Tortuga LDR passives and see the light!
However, I think the vast majority of audio enthusiasts are quite convinced that the only good preamp is an active preamp - evidence to the contrary notwithstanding. Thus a buffer option opens up the possibility of appealing to a larger market that may be willing the embrace the benefits of LDRs as long as it comes with the requisite familiar buffer/gain (i.e. it's an active preamp). Said differently, give the customer what he wants. Of course then there's Steve Jobs who said the customer doesn't know what he/she wants until you give it to them. Perhaps a buffer/gain bypass switch is in order. :green:
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- Avoiding to use switching regulators: at least giving this as a paid option, eg using Belleson regulators.
I will disagree as to the idea that switching regulators are somehow inherently inferior to linear regulators in audio applications. The regulator we currently use is actually quite a nice bit of hardware and far superior to the ubiquitous LM9XXX series we used in the V1 model. That said, it's certainly not a super-regulator like the Belleson. Which by the way we are in the process of evaluating. Also, more recently there are some newer ultra low-noise linear regulators from TI and others that rival super-regulator performance. All of those are surface mount components. Also, anyone daring enough with a solder iron can swap out the existing regulator for a Belleson. Just get one with a LM78xx pin configuration and around 400-500 ma capacity. Be very careful removing the existing regulator which is rather beefy - easy to bugger the pads or lift a trace.
How's the preliminary testing with the Belleson 5v regulators in place of the switching supply.
There are some <0.8uv regs that you mentioned, woud these be better than Belleson, newclassD, Hynes supplies. It seems that these new regs have finally come up with some excellent specs.
As i am already using a low noise supply feeding 12v to the boards and wonder if there is much room for improvement.
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How's the preliminary testing with the Belleson 5v regulators in place of the switching supply.
I'll know more by the end this week and will update then.
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I have successfully swapped the 5v with a tps7a4700 low noise unit, its sharing a 5v output for both channels. Time for some fun.
performance wise it it worth while adding a small tantalum or maybe 20uf electrolic to each ldr unit soldered directly to the legs?
We'll share the resjlts this weekend :thumb:
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I have successfully swapped the 5v with a tps7a4700 low noise unit, its sharing a 5v output for both channels. Time for some fun.
performance wise it it worth while adding a small tantalum or maybe 20uf electrolic to each ldr unit soldered directly to the legs?
We'll share the resjlts this weekend :thumb:
The TPS714700 has great specs but I believe it only comes in a tiny 5x5mm VQFN surface mount. How did you package it up to fit the LM78xx/T220 3 hole spot where the stock regulator lived?
I don't think there's anything to be gained by putting a cap across the LED (control) legs of the LDRs. That's essentially a steady state DC signal that only changes when changing volume.
Iv'e suspected for some time now that the upstream 2 stage op amp introduces quite a bit of noise. It's a lowly quad LM324 which has been around forever and is a workhorse single voltage opamp. The LDR3x uses it, along with a reference voltage, to bracket the lower and upper limits of control voltage to the LDR which is driven by DACs upstream of the op amps. We run the output of the main gain stage into an adjacent op amp used only as a unity gain buffer. Frankly I don't know why we added the buffer but like all design decisions it seemed like the right thing to do at the time - and it was there anyway for the using. The buffer really isn't needed and I think it introduces considerable noise; at least in this op amp. I've been meaning to try bypassing that buffer opamp which would probably require cutting the legs off the buffer end of that chip and then adding a short jumper to connect the output of the gain stage to the where the output of the buffer would've been. This would end up looking like a messy tweak but I suspect it would reduce noise on the control signal to the LDR.
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I cut the swithing regs out and yes, the tps7a4700 is on its own board which i wired to the 5v connections.
There is better microdetailing which i believe is due to improvement in noise, no change to tonality.
I bought it of ebay andit worthwhile improvementm costing slightly more than the switching regs, but i share the 5v for my balanced boards.
How was the belleson reg?
Also can you detail the bypassing of the buffer,how do i hardwire to bypass.
Im all in for your next improved board, it's fantastic as it is now.
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Hi Morten,
I looked up the lm324. Its a 4 channel with + and - for each channel's output.
To bypass, do i join the inputs + and - for each cannel to its respective single output (1 to 4) and cut pin 4 which is vcc.
Is there any other considerations with removing the buffer?
Would replacing will a OPA4134 be any use?
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Hi Morten,
I looked up the lm324. Its a 4 channel with + and - for each channel's output.
To bypass, do i join the inputs + and - for each cannel to its respective single output (1 to 4) and cut pin 4 which is vcc.
Is there any other considerations with removing the buffer?
Would replacing will a OPA4134 be any use?
To isolate and bypass the buffer op amp sections I would pull the lm324s and cut off pins 5, 6, 7, 8, 9, 10. Those are the pins on the end facing the LDRs. Then I would try to insert jumpers between pin sockets 5 and 7, and between 8 and 10. Put the clipped LM324 back in their sockets making sure the stub ends of the clipped off pins are not touching the jumpers you put in the sockets.
To be clear I've yet to try this but it should work. Worst case you bugger up a pair of op amps that cost 25 cents each.
I don't think the opa4134 would work since it doesn't appear to be suited for single supply operation. There are surprisingly few substitutes for the lowly Lm324. The few bipolars I've tried have not worked. I suggest first confirming whether the above bypass helps before rolling op amps. This is purely a steady state DC application of this op amp so things like speed aren't really relevant. Stability, low noise and PSRR should be all positives.
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Therr are 2 lm324 per board and the pins are not facing the ldrs.
You have specified channels 2 and 3 in each lm324 , which are both rows closest to the ldrs
Please clarify.
Also is there any testing to be done or if it sound worst just reconnect the clipped pins.
I dont quite understand what a buffer with and with does for the signal or power.
Thanks
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Therr are 2 lm324 per board and the pins are not facing the ldrs.
You have specified channels 2 and 3 in each lm324 , which are both rows closest to the ldrs
Please clarify.
Also is there any testing to be done or if it sound worst just reconnect the clipped pins.
I dont quite understand what a buffer with and with does for the signal or power.
Thanks
There are 4 LDRs - 1 series & 1 shunt per left/right channel. Each op amp serves a channel. One side of op amp serves the series LDR and the other side the shunt LDR.
While it remains unproven, I submit that bypassing the op amp buffer stage to each LDR may reduce the noise and thus improve performance. I've had this on my "to try" list for some time but simply have not gotten around to it - too much other stuff to do. If you're looking for a potential tweak - this is the one I recommend someone try and let us know what you think.
I don't know why but after the V2 design was set and production boards were made I noticed that there was way more noise on the buffer stage output than there should be. Said differently, there's far less noise on the input to the buffer stage than the output. We do add a 0.1 uF bypass to the output pin to help reduce this. So why not just bypass the buffer stage and see if there's a benefit? That's the proposed tweak. As to why we ran the control signal through a buffer stage at all? Let's just file that under "it seemed like the right thing to do at the time" and move on.
Worst case is you try this on your V2.1 board, there's not discernible benefit and you've ruined a pair of 25 cent op amps for nothing - such is life. Best case scenario is you confirm a relatively easy tweak that improves the sound via noise reduction - hooray!
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There are 4 LDRs - 1 series & 1 shunt per left/right channel. Each op amp serves a channel. One side of op amp serves the series LDR and the other side the shunt LDR.
While it remains unproven, I submit that bypassing the op amp buffer stage to each LDR may reduce the noise and thus improve performance. I've had this on my "to try" list for some time but simply have not gotten around to it - too much other stuff to do. If you're looking for a potential tweak - this is the one I recommend someone try and let us know what you think.
I don't know why but after the V2 design was set and production boards were made I noticed that there was way more noise on the buffer stage output than there should be. Said differently, there's far less noise on the input to the buffer stage than the output. We do add a 0.1 uF bypass to the output pin to help reduce this. So why not just bypass the buffer stage and see if there's a benefit? That's the proposed tweak. As to why we ran the control signal through a buffer stage at all? Let's just file that under "it seemed like the right thing to do at the time" and move on.
Worst case is you try this on your V2.1 board, there's not discernible benefit and you've ruined a pair of 25 cent op amps for nothing - such is life. Best case scenario is you confirm a relatively easy tweak that improves the sound via noise reduction - hooray!
My curiosity couldn't stand it any longer so I just went ahead and tried this mod. Don't bother. I put a scope on it before/after and there was no change which is as it should be. I believe the noise issue I was seeing earlier had more to do with instrumentation ground loops than anything else. I made sure there were none this time and so no change. Save your op amp and don't try it. The good news is the noise on the control signal to the LDR's is down around +/- 5 mv which considering the regulator is on the order of +/- 10 mv is not all that surprising.
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Thanks Morten,
i didn't stand a chance, quickest hand draws first. Thanks for the update so we shall leave it as it is.
Just wondering how the belleson reg turned out in your testing.
So the v2.1 ias it stands is as great as it can :thumb:
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While still very much early stage, version 3 (V3) of our LDR preamp controller system is taking shape.
A key departure with earlier versions (V0, V1, V2 & V2.1) is the V3 will physically divide the preamp controller into 2 different board types; the Controller Board ("CB") and the LDR Board ("LDRB"). The CB will do most of the work and is the "smart" board that communicates with both the LDRB as well as the outside world (i.e. the user). The LDRB will contain the actual LDRs for one left/right single-ended stereo channel. The LDRB will simply respond to commands from the CB. The CB and the LDRB will communicate over a simple I2C network.
By breaking this preamp controller system into 2 board types it will be much easier and much less costly to implement multi-channel systems. For example a balanced audio preamp would require only 1 CB but 2 LDRBs. If you wanted to add additional stereo channels you would just add more LDRBs. This approach would definitely make bi or tri-amping more practical including multi-channel DAC attenuation.
As currently conceived, all power will come from the CB which would have separate digital and analog voltages which would be distributed to the LDRBs. Connections between the CB and one or more LDRBs would be via daisy chained 2x5 ribbon cable connectors so they could be physically arranged/distributed as desired.
Both board types will utilize mostly surface mount components which should make everything smaller yet there will still be various pin connectors to a host of external devices as before. At this point it appears we have eliminated the use of op amps entirely along with a good number of related resistors. Hopefully that won't change. Changing from 12 bit to more flexible 16 bit DAC/ADCs has helped simplify and further reduce total parts count while bumping up the overall accuracy of the controller which can only help improve sound quality.
While nothing is set in stone yet, the V3 will likely have Bluetooth communications in addition to the existing IR/remote functionality which means it will be controllable via most iOS/Android phones via a custom control app.
The LDR/audio signal end of things is not going to change much from the V2/V2.1 except that the audio in/out of both channels will have optional isolation LDRs that will function as on/off switches in lieu of relays for isolating the LDRB during auto-calibration. If the LDRB is connected to multi-input switching devices these may not be required hence the reference to "optional". The auto-cal isolation relay will continue to be a conventional relay but is not in the signal path during normal operation (same as now).
The V3 is still quite a ways off and I'm not going to even begin to speculate on timing. Questions and comments welcome as always.
On a final note, I don't envision the V3 being something that existing owners of earlier V2/V2.1 systems should feel compelled to upgrade to because as things stand now I don't have any expectations that the V3 will improve on the overall sound performance - which is already quite amazing. :thumb:
(http://www.tortugaaudio.com/images/v3_system_network_1.jpg)
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An audiophile/HT wet dream for sure! Keep at it Morten, I'll be one of your 1st customers...
Best,
Anand.
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Would it be possible to program a phase reversal switch into the software?
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Would it be possible to program a phase reversal switch into the software?
This is the second inquiry on this topic today. Just got off a phone call about this for a balanced unit.
Phase reversal is relatively straight forward with balanced audio since you are already dealing with 2 signals, each 180 degrees out of phase with respect to each other. These are on pins 2 and 3 of XLR connectors. To reverse phase you can simply reverse their connection. I'm looking into how best to do this with our balanced units using the existing hardware. One approach is to connect a pair of inputs to 2 different input board channels with one channel wired "normal" (2 - 2, 3 - 3) and the other wired reversed (2 - 3, 3 - 2). By switching between these 2 inputs you are reversing the phases of the same input.
When it comes to single ended audio the only way I can think of to actually reveres the phase is to either run the inputs through inverted op amps or through transformers. This isn't something that can done with the stock hardware. You could run an input into two different inputs with one going through a transformer which would reverse its phase and the other connected normally. Then it would be a matter of simply switching inputs as to which phase sounds best.
If anyone else has other ideas or perspectives on this would love to hear your thoughts.
Cheers,
Morten
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I like the V3 design... Keep allowing Apple remote for power and volume and I am in to upgrade my V1.2 : )
I used an Apple iPhone/iPad/usb charger for my power, what about adding usb for power too? Possibly you could drop the wall-wart?
Thanks and keep up the great work!!!
C
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I'll fess up that I'm the guy who's been bending Morten's ear on the topic of absolute polarity reversal. I'm currently relying on the DAC to handle that, but there are DACs that don't have that option or only via a switch on the front panel. Having that feature on the preamp would also work on inputs from phono stages.
My request is for polarity control on at least one input, though Morten indicated that the architecture of the LDRxB could handle multiple inputs with polarity control. Since I use a fully balanced system, DAC to power amps, the limitation of this control to balanced units is not an issue for me. I would want the polarity control on the remote, since selecting the correct setting for each particular recording is best done from the listening position. Also of importance is that the switch be easily and quickly made from the remote, not buried in a secondary menu level as is sometimes the case with DACs. Apparently some manufacturers assume that a user would only need to choose a setting once when setting up the system, which is definitely not my experience.
Lastly, it would be useful to have some sort of indicator on the display. Even a few pixels would be enough, on or off corresponding to the polarity selected. Another thought is to use different brightness levels for the left and right volume settings with the left display brighter then the right and vice versa when polarity is inverted. That wouldn't require differences in the display hardware.
As far as how to manage adding another control function to the Apple remote, my suggestion is to use the play/pause button for phase reversal. I notice that when I want to mute the audio that I use the menu button. It works just as quickly as the play/pause button and I've not heard any change in sound when bringing the audio back up from the "off" state. It's my understanding that even when the menu button is activated that the LDRs are not fully turned off. Perhaps Morten could illuminate (pardon the pun) the difference in the state of the LDRs between "off" via the menu button and "muted" via the play/pause button.
I realize there may be customers who would not be interested in polarity inversion. Would it be possible to have a control function that would activate/deactivate it? My suggestion is to use a long-press of the play/pause button to activate/deactivate polarity inversion control. If the customer didn't want to use the feature, the play/pause control would work as it does today in the default configuration until activated.
My experience with implementations of polarity inversion control in the analog domain, such as a switch on a preamp, has been that when the inverted setting is activated, the signal often goes through additional switches and/or circuitry that compromises the sound compared to the non-inverted mode. From discussions with Morten, this would not be the case with the Tortuga implementation.
Thanks again to Morten for his openness to customer feedback and suggestions.
Best,
Robert
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I like the V3 design... Keep allowing Apple remote for power and volume and I am in to upgrade my V1.2 : )
I used an Apple iPhone/iPad/usb charger for my power, what about adding usb for power too? Possibly you could drop the wall-wart?
Thanks and keep up the great work!!!
C
The V3 design continues to evolve since the last post on the subject. We've done away with a separate controller board and are staying with the same concept as with the V2 where a single LDR board can serve as both master or slave based on flipping a jumper. The earlier idea of having 2 different board types added complexity while really not saving much in cost. The key difference between the V2 and this V3 prototype is the adoption of I2C networking which will allow for up to 16 separate stereo channels - way more than will likely ever be used. Meanwhile each board is self-contained so the board-to-board network interface remains a simple 2 wire daisy-chained serial connection.
Being a software driven system, there will inevitably be cause to upgrade the firmware. One challenge with multiple networked boards is we want to avoid having to update each board individually as is the case with our V2 design. With the V3 we want to only have to update the master firmware and then have the master automatically handle updating the firmware on any other slave boards present. That's all doable but we have yet to do the development work.
I've included a snapshot below of the current V3 layout. This will undoubtedly change as we refine the design but I think we'll be able to keep the board to roughly 2.5" x 2.7" as shown with most IC and discrete components being surface mount. That's literally 50% smaller than the V2 board. AND there's no secondary piggyback board as there is with the V2 so this will be a much lower profile board.
Those with an eagle eye and design experience will note 2 voltage regulators side by side labeled 7805 and 317. We don't intend to use either of these established regulators but instead are exploring the use of both our own as well as third party high performance discrete and semi-discrete drop-in regulators that use the same 3 terminal through-hole footprints as either of those regulators. Also, the V3 will definitely use separate digital and analog power.
Cheers,
Morten
(http://www.audiocircle.com/image.php?id=123179)
(http://www.audiocircle.com/image.php?id=123180)
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Has anybody tried using batteries for the power supply?
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Re a battery power supply, I've purchased an Optima marine battery for that purpose. It's way overkill for the current draw of my LDR1B, but if I ever need to jump a car or tractor, it will do the job. I'm going to use a trickle charger connected to a remote controlled AC relay that I can turn off when I'm listening and on when I'm not. I'd like to find a relay that can use the 12v trigger output of the LDR1B. I need the trigger-on to turn off the relay and the trigger-off turning it on. I think the LDR1B is a perfect candidate for battery power supply this since it uses a wall wort for DC power instead of the internal power supply conversion in the LDRxB. I just need to salvage the input connector from another wall wort for a forgotten device from the past. I just haven't gotten around to wiring up the battery since the LDR1B sounds so good as is.
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I agree the Tortuga sounds great as is but audionervosa creeps in just enough to be curious if off-the-grid power would make any difference. I will be looking forward to your experimenting with that Optima battery.
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Has anybody tried using batteries for the power supply?
Funny you should mention it. This question of performance on battery has been burning a hole in my curiosity pocket for a while now. Especially since KernelBob went out and bought a big honk'n marine grade battery to try this on his LDR1B.
Yesterday I went out and bought a 10 AHr 12 V battery and have had it running on a Tortuga V2.1 board for the past 24 hours while turned on with dual displays. It went from 12.56 to 12.15 volts over that time period so plenty of capacity relative to load. Tied to a recharge circuit my guess is you could listen to music nonstop for a couple of days before you'd need to kick in recharge. That size battery fits inside the same enclosure as the LDR1B or LDR3.V2.
Today I spent some time taking measurements of the command signal to an LDR under various power supply scenarios. While not exhaustive or definitive I think the following findings are valid:
1) Most of the noise/hash in the control signals to the LDRs is a combination of the 5 V switch mode DC converter on the controller board plus the microcontroller. The DC converter runs somewhere above 100khz and the microcontroller runs at 4 MHz. The net of this is vey roughly +/- 10 millivolt noise way outside the audio band.
2) I saw no change in this whether I powered the board from a 12 V switch mode supply or from the 12 V battery. Keep in mind that the board uses both the raw 12 V supply as well as 5 V from an on board switch mode regular.
3) Next I removed the pricey on board 5 V DC switch mode regulator which has really good specs BTW and replaced it with a cheap (25 cent) LM7805 linear regulator and then ran the board off the battery. This cut the high frequency noise/hash by 50% to 5 millivolts. I suspect that the reduction was due to the elimination of the switch mode regulators switching noise up in the 100's of kHz.
All fine and good but did the battery plus cheap linear regulator help the performance? Honestly, I don't know. It sure sounded nice but then again....it always sounds nice!
Then I ran autocal with the battery/cheap linear regulator to see if anything changed with the reduced high frequency noise. It DID! Autocal ran smoother and faster. This was with the stock autocal op amp and not the upgrade. Autocal being a closed loop instrumentation circuit this makes general sense since signal noise will impact performance.
Too early to draw definitive conclusions but this suggests the unit would be happier with pure DC supply and no switch mode noise. Audible? Too soon to say.
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Addendum: 6.22.15
I added the pics below showing the change in the control signal noise. The first one is the "Before" which is with our own 12 VDC supply and the stock 5 VDC regulator on the board. The second graph shows the "After" when I replaced the stock 5V switching regulator with a cheap LM7805 linear regulator and powered the board with a 12 VDC battery.
The scale on the left is in millivolts and the time scale is in microseconds so each major tic is 1 MHZ. This high frequency noise is no doubt induced by the microcontroller running at 4 MHZ effective with a 16 MHZ crystal.
There's noise that matters and then there's just noise. Arguably, this noise is so far out of the audible range as to be irrelevant. Plus in order for this to be "heard" by the audio side of the LDRs, the LDR photoresistors would have to have a comparable bandwidth which they definitely do not. The reaction time of LDRs to changes in LED current/brightness is a few millisconds and not microseconds. Said differently, the LDRs filter out this noise.
(http://www.audiocircle.com/image.php?id=123211)
(http://www.audiocircle.com/image.php?id=123212)